Broiling the marshmallows right to the brink of charred gives these bars a smoky taste reminiscent of a campfire cookout. Keep an eye on the marshmallows through the oven door as you would with marshmallows over a fire — charred is good, burnt is bad.
Campfire Marshmallow Bars
Position an oven rack 6 inches from the broiler element. Heat the oven to broil, on a medium setting, if possible, and turn on the oven light. Put the cereal in a large bowl.
Scatter the butter in a 13- by 9-inch cake pan and place in the oven to cook until the butter melts and its milk solids turn light golden brown, 3 to 5 minutes. Watch it carefully. Immediately remove the pan from the oven and carefully tilt it to evenly coat the bottom with the butter. Quickly spread the marshmallows in a single layer in the pan.
Return the pan to the oven rack and broil, watching the progress the whole time, until the tops of the marshmallows are very dark golden brown and the marshmallows are puffed, 2 to 4 minutes. Carefully and immediately slide the marshmallows out of the pan and into the bowl with the cereal. Leave behind any butter slicking the pan; don’t scrape anything out.
Carefully fold the marshmallow mixture together until the cereal is evenly coated. Scrape the mixture into the pan and press it in an even layer. Cool completely, then cut into 24 bars to serve.